Polyvinylidene fluoride (PVDF) is a chemically resistant engineering plastic. PVDF and its copolymers have been used in many high performance applications. While PVDF films can be made to be transparent, they still have some degree of haziness, producing a product that is less than optically clear. There is a need for an optically clear PVDF or PVDF copolymer that retains the chemical resistance of PVDF
U.S. Pat. No. 5,140,082 discloses a vinylidene fluoride/trifluoromethyl ethylene copolymer (3,3,3-trifluoropropene)(TFP). Synthesis by bulk, solution, suspension and emulsion polymerization are described, with all the TFP in the initial charge. The copolymer has excellent weather resistance, corrosion resistance and electrical characteristics. The reference is silent on optical clarity.
US 2007/0232769 describes the emulsion polymerization of a copolymer of tetrafluoroethylene (TFE) and TFP. The copolymer is produced in a semi-batch process, with most or all of the TFP is added as a delayed feed, and the copolymer produced has excellent processability. The reference is silent on optical clarity.
Surprisingly it has been found that copolymers of vinylidene fluoride and 3,3,3-trifluoropropene can be synthesized by a semi-batch emulsion polymerization process, with the copolymers produced having excellent optical properties. Additionally films of the copolymer are extremely flexible and tough, and have a high melting point.